6. Lepidium draba L. (heart-podded hoary cress, heart-podded white top)

Cardaria draba (L.) Desv.

Pl. 318 a, b; Map 1365

Plants perennial herbs, with long-creeping, branched rhizomes, often forming dense colonies. Stems (8–)20–65(–90) cm long, erect or ascending, branched in the upper third, densely pubescent, sometimes the upper portion becoming nearly glabrous at maturity. Lowermost leaves petiolate, (1.5–)3.0–10.0(–15.0) cm long, obovate to oblanceolate, the middle and upper leaves sessile, clasping the stem with rounded auricles, densely pubescent, ovate or oblong to oblanceolate, (1–)2–8(–10) cm long, dentate or nearly entire. Inflorescences flat-topped panicles or racemes, not elongated in fruit. Sepals 1.5–2.2 mm long, oblong. Petals white, (2.5–)3.0–4.0(–5.0) mm long. Stamens 6. Styles (0.8–)1.0–1.8(–2.0) mm long. Fruits (2.5–)3.0–5.0 mm long, cordate or ovate, strongly indented or grooved at the replum, rounded or obtuse to truncate at the base, the valves not inflated, flattened, glabrous, keeled, not winged, prominently veined, the fruit stalk 4.5–11.0(–14.5) mm long. Seeds 1.5–2.0 mm long, not winged, the surface with a relatively prominent but fine, netlike or honeycomb-like pattern of ridges and pits, dark brown. 2n=32, 64. April–July.

Introduced, sporadic (native of Europe, Asia, widely introduced in the U.S. and Canada). Roadsides, railroads, and open, disturbed areas.

Lepidium draba and L. chalepense differ only in fruit size and shape. Partially fertile hybrids have been said to occur in Canada, but no experimental documentation has been published to date. The two are often treated as subspecies of a single species. The hoary cresses (L. appelianum, L. chalepense, and L. draba) are considered noxious weeds in some western states, where they are weeds of crop fields and pastures and also invasive in natural plant communities.